Exemplary embodiments relate generally to a semiconductor memory device and, more particularly, to a semiconductor memory device and a method of operating the same, which can influence capacitive coupling between word lines.
High-capacity semiconductor memory such as, for example, NAND flash memory has been in the spotlight due to its potential for replacing a hard disk drive. The NAND flash memory device is characterized in that it facilitates high capacity and high degree of integration and retains information even when power is not supplied to the NAND flash memory device. The memory cell of the NAND flash memory device has a dual gate structure including a floating gate and a control gate. Data is stored or erased in the memory cell due to electrons going to or from the floating gate using an FN tunneling effect according to a potential difference between the control gate and a channel body.
The control gate is coupled to a word line and controlled in response to voltage supplied to the word line. The channel is coupled to a bit line and configured to control a channel voltage by controlling the voltage of the bit line. The NAND flash memory device performs a program operation of storing data in memory cells by controlling the voltages of a word line and bit lines. The threshold voltage of the memory cell is shifted according to the number of electrons stored in the floating gate, and data is stored in the floating gate using the shifted threshold voltage.
The voltage of a local word line coupled to the memory cell is controlled using a global word line. The voltage of the local word line is controlled by a word line precharge operation of transferring a high voltage to the local word line and a word line discharge operation of changing the voltage of the local word line to a low voltage. Almost all the operations of the NAND flash memory device include the word line precharge and the word line discharge operation.
A read operation of the NAND flash memory device is a very basic operation, and used often. If there is a problem in the read operation, the problem has a great effect on the NAND flash memory device. The word line discharge operation in the read operation is very important. If voltage supplied to a word line coupled to a memory cell to be read is low, the voltage of the word line is greatly influenced by the voltages of surrounding word lines. This effect is greater in the word line discharge operation than in the word line precharge operation. This phenomenon is generated by capacitive coupling between the word lines. Consequently, the word line discharge operation in the read operation has a great effect on the threshold voltage distribution of the memory cells.
Accordingly, there is a need for a method of preventing a change in the threshold voltage distribution of memory cells that may be generated in the word line discharge operation during the read operation.